Referring to FIG. 12, conventional bearing devices for driving wheels have a rolling bearing 2 fitted around an outer periphery of a hollow shaft portion 12 of a hub wheel 1 to which a wheel can be fitted. The hub wheel 1 is tiltably coupled with a shaft 7 by a constant velocity joint 3. A shaft end on the vehicle inner side of the hollow shaft portion 12 in the hub wheel 1 is bent and deformed radially outward to constitute a caulked portion 12a to be caulked on an outer end face of an inner ring 25 of the rolling bearing 2 so that the inner ring 25 is thereby preloaded and prevented from falling out.
An outer ring 31 of the constant velocity joint 3 comprises a cup-shaped cylindrical portion 35 which is used as a raceway for a group of balls for tilting guide and a shaft portion 36 which is inserted into the hollow shaft portion 12 of the hub wheel 1 so as to be spline fitted to a small diameter portion of the cup-shaped cylindrical portion 35.
The cup-shaped cylindrical portion 35 of the constant velocity joint 3 is abutted on the caulked portion 12a formed by the radially outward bent and deformed shaft end on the vehicle inner side of the hollow shaft portion 12 in the hub wheel 1. The constant velocity joint 3 is connected to the hub wheel 1 with a nut 36i fastened in the manner in which an end face of the nut 36i screwed into a small diameter screw shaft portion 36h on the vehicle outer side of the outer ring shaft portion 36 of the constant velocity joint 3 contacts with an end face of an opening 12c on the vehicle outer side of the hollow shaft portion 12 in the hub wheel 1.
The hub unit described above generally, through caulking the vehicle inner side end portion of the hub wheel 1 on the outer end face of the inner ring 25 of the rolling bearing 2, imparts the preload to the rolling bearing 2.
In such conventional bearing devices, the constant velocity joint 3 is connected to the hollow shaft portion 12 of the hub wheel 1 in the manner in which no rattle in the axial direction is generated. Thus, fastening the nut 36i too tight would result in an excessive preload with respect to the rolling bearing 2 via the caulked portion 12a, leading to the likelihood of an adverse effect on a rolling performance of the rolling bearing 2.
Therefore, a main object of the present invention is to provide a bearing device wherein a constant velocity joint can be connected to a hub wheel without imparting an excessive preload with respect to a rolling bearing.